It is appreciated that Uranium Hexafluoride (UF6) is useful for its intended purpose. However, exposure of this substance to the general public can be quite hazardous, and accordingly there is a need to ensure containment, especially during transportation. Currently, Uranium Hexafluoride is stored and transported in conventional cylinders, like conventional cylinders ANSI N14.1 30B or 30C cylinder. Regulations require that cylinders be stored in approved protective shipping packages (PSP) during transportation, which limits exposure of the container to hypothetical accident conditions. Hypothetical accident conditions refer to potential situation where the PSP could be dropped, subjected to a fire event, immersed in water, or otherwise damaged. The primary concerns are critical events or release of radioactive materials.
Natural UF6 contains the isotope U235 in a weight percent of 7/10 of one percent. The isotope U235 emits neutrons and, in the enriched state, gives UF6 is radioactive characteristics. Enriched UF6 has a weight percentage of the U235 greater than 7/10 of one percent. The industry standard for the commercial use of enriched UF6 includes weight percentages extending up to five percent. In the enriched state, UF6 can become critical given the right circumstances, for which the chance of becoming critical increases with the amount of U235 present. Moderators slow the movement of emitted neutrons thereby increasing the possibility of a collision, which can trigger a critical event. Persons skilled in the art refer to the Keff factor, where a Keff greater than 1.0 relates to a condition where the number of neutrons are increasing resulting in a critical event. Conversely for a Keff less than 1.0, neutrons are being absorbed. Water is one such moderator of UF6. Accordingly, it is important to ensure that UF6 does not become exposed to water or water based substances. If the storage container valves and plugs become damaged and/or deteriorate, the possibility of contact with water significantly increases, as does the possibility of a critical event.
One factor contributing to a critical event pertains to the amount of U235 present within a cylinder. Of course, the amount of any substance that can be stored in a given container is limited by the container's construction, namely the dimensions of the cylinder walls. For precautionary reasons, regulations limit the weight quantity of U235 that can be stored in a container to five (5) weight percent of the total volume of material stored in a cylinder. However, in recent years the industry has been desirous of shipping and storing enriched UF6 containing U235 in weight percentages in excess of five (5) percent.
Currently, the state of the art does not provide a cylinder that is safe by geometry incorporating an annulus base and having a Keff less than 1.0. A need therefore exists to provide containers for transporting enriched UF6 having U235 between five weight percent and twenty weight percent. Advantages of the embodiments of the subject invention will become apparent to those skilled in the art.